DEBT - Short-Term Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025	Jun. 30, 2025
Short-term Debt [Line Items]
Balance Outstanding	$ 121,289	$ 171,989	$ 157,396
NW Natural
Short-term Debt [Line Items]
Balance Outstanding	0	9,990	0
Commercial Paper
Short-term Debt [Line Items]
Balance Outstanding	$ 105,300	$ 162,000	$ 157,400
Weighted average interest rate (as percent)	4.10%	4.10%	4.80%
Commercial Paper \| NW Natural
Short-term Debt [Line Items]
Balance Outstanding	$ 0	$ 10,000	$ 0
Weighted average interest rate (as percent)	0.00%	4.00%	0.00%
SiEnergy Credit Agreement Loans \| SiEnergy
Short-term Debt [Line Items]
Balance Outstanding	$ 16,000	$ 0	$ 0
Weighted average interest rate (as percent)	4.70%	0.00%	0.00%

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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Name:	us-gaap_ShortTermBorrowings
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant